Data carrier for storing information represented by an information voltage

ABSTRACT

In a data carrier ( 1 ) that is arranged to receive a signal (S) in a non-contacting manner, there is provided a circuit ( 2 ) that is arranged, by using the signal (S), to generate a supply voltage (V) for parts of the circuit ( 2 ), the circuit ( 2 ) having a storage stage ( 5 ) that is arranged to store information capacitively, the information being represented by a value of an information voltage (UI) arising at the storage stage ( 5 ), and the circuit ( 2 ) having an information-voltage generating stage ( 6 ) that is arranged to receive a control signal (CS), which control signal (CS) is of a voltage value that is at most equal to the value of the supply voltage (V), and that is arranged to generate the information voltage (UI) by using the control signal (CS), wherein the information-voltage generating stage ( 6 ) has a voltage-raising stage ( 8 ) that is arranged to raise the value of the voltage of the control signal (CS).

The invention relates to a data carrier that is arranged to receive asignal in a non-contacting manner and that has an electrical circuit, towhich circuit the signal can be fed and which circuit is arranged togenerate a supply voltage for parts of the circuit by using the signal,which circuit comprises storage means that are arranged to storeinformation capacitively, the information being represented by a valueof an information voltage arising at the storage means, and whichcircuit comprises information-voltage generating means that are arrangedto receive a control signal, which control signal is of a voltage valuethat is at most equal to the value of the supply voltage, and that arearranged to generate the information voltage by using the controlsignal.

The invention further relates to a circuit for a data carrier, whichdata carrier is arranged to receive a signal in a non-contacting manner,to which circuit the signal can be fed and which circuit is arranged togenerate a supply voltage for parts of the circuit by using the signal,which circuit comprises storage means that are arranged to storeinformation capacitively, the information being represented by a valueof an information voltage arising at the storage means, and whichcircuit comprises information-voltage generating means that are arrangedto receive a control signal, which control signal is of a voltage valuethat is at most equal to the value of the supply voltage, and that arearranged to generate the information voltage by using the controlsignal.

A data carrier of the kind described in the first paragraph above and acircuit of the kind described in the second paragraph above are knownfrom the published draft ISO/IEC CD 18000 of the ISO/IEC 18000 standardthat is currently being produced.

The known data carrier that has the known circuit and that is arrangedto receive, in a non-contacting manner, a signal emitted by a read/writestation, it being possible for a supply voltage for parts of the circuitto be generated by the circuit by using the signal, has storage meansthat are formed by a capacitor and that are arranged to storecommunication-related information relating to communication between thedata carrier and the read/write station, in which case thecommunication-related information is intended to be capable ofevaluation for a period of time. The information is represented by avalue of an information voltage that arises at the capacitor. Alsoprovided are an n-channel field effect transistor that forms aninformation-voltage generating means, and a current source, these twoitems being arranged in series with one another and being connectedbetween the capacitor and the supply voltage, it being possible by meansof them and by using a digital control signal that can be fed to thecontrol electrode of the transistor for the capacitor to be charged to avalue of the information voltage that is reduced from the value of thecontrol signal voltage by an amount equal to a characteristic transistorthreshold voltage that is present between a point of connection of thetransistor to the capacitor and the control electrode of the transistor.The digital control signal is of a voltage value that is at most equalto the value of the supply voltage.

With the known data carrier, there is the problem that, at the time whenit is generated, the value of the information voltage is lower than thevoltage value of the control signal and that, following the generationof the information voltage, there is a continuous decline in the valueof the latter because the capacitor is constantly being discharged byunavoidable leakage currents in the circuit. This produces theunsatisfactory situation that, as a function of the supply voltageavailable at the time when the information voltage was generated and asa function of the size of the leakage currents, the information storedby means of the capacitor is no longer able to be evaluated after only ashort period of time.

It is an object of the invention to remedy the problems detailed abovein a data carrier of the kind described in the first paragraph above andin a circuit of the kind described in the second paragraph above and toprovide an improved data carrier and an improved circuit.

To achieve the above object, provision is made, in accordance with theinvention, in a data carrier of the kind described in the firstparagraph above, for the information-voltage generating means to havevoltage-raising means that are arranged to raise the value of thecontrol-signal voltage.

To achieve the above object, provision is made, in accordance with theinvention, in a circuit of the kind described in the second paragraphabove, for the information-voltage generating means to havevoltage-raising means that are arranged to raise the value of thecontrol-signal voltage.

What is achieved in an advantageous manner by the provisions made inaccordance with the invention is that the information voltage arising atthe storage means can assume substantially the value of the supplyvoltage virtually irrespective of the transistor threshold voltage orthe value of the control-signal voltage. This also gives the advantagethat the entire difference in voltage between a reference potential andthe supply voltage can be used to represent the information, thus givinga maximum possible signal-to-noise-voltage ratio for evaluating theinformation. Particularly when there are leakage currents present, thisgives a substantially longer period of time during which the storedinformation can be ascertained with high reliability, which means thatthe stored information can still be evaluated even after a briefsupply-voltage failure and, by the use of the information, communicationbetween a read-write station and the data carrier can continue evenafter a supply-voltage failure of this kind without the communicationconnection having to be completely re-made.

In the case of the solutions according to the invention, provision mayfor example be made for the voltage-raising means to be formed by avoltage source that can be operated to float in relation to a referencepotential of the circuit by which the value of the control-signalvoltage can be raised by a desired amount. It has however provedparticularly advantageous if the features detailed in claim 2 and claim5 are provided in the respective cases. This gives the advantage that,using the supply voltage, a reliable increase can be made in the valueof the control-signal voltage in a manner that is as simple andinexpensive as possible to put into practice.

In the case of the solutions according to the invention, it has alsoproved advantageous if the features detailed in claims 3 and 6 areprovided in the respective cases. This gives the advantage that, whenthe value of the control-signal voltage is raised, the voltage valuethat arises is only such a one as the information-voltage generatingmeans can use to generate the information voltage without any problems.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiment described hereinafter.

IN THE DRAWINGS

FIG. 1 is a diagrammatic block circuit diagram of one embodiment of datacarrier according to the invention.

FIG. 2 is a view similar to FIG. 1 showing a first detail of the datacarrier according to the invention shown in FIG. 1.

FIG. 3 is a view similar to FIG. 1 showing a second detail of the datacarrier according to the invention shown in FIG. 1.

FIG. 4 shows a circuit implementing the second detail of the datacarrier according to the invention shown in FIG. 1.

Shown in FIG. 1 is a data carrier 1 that is arranged for non-contactingcommunication with a communication station that is not shown in FIG. 1.For this purpose the data carrier 1 is arranged to receive a signal Sfrom the communication station in a non-contacting manner, the signalbeing formed by a high-frequency carrier wave so that the data carrier 1can be supplied with energy by means of signal S. It is also possiblefor enquiry information to be communicated from the communicationstation to the data carrier 1 by means of the signal S, in which casethe signal is an amplitude modulation of the carrier wave. It is furtherpossible for answer information to be communicated from the data carrier1 to the communication station by means of signal S, in which case thesignal is a load modulation able to be produced by the data carrier 1.

The data carrier 1 has an electrical integrated circuit 2. The circuit 2has components of transmit/receive means 3 that are arranged to receivethe signal S. For this purpose the transmit/receive means 3 have atransmission coil configuration (not shown in FIG. 1) that is coupled tothe circuit 2, thus enabling the signal S to be fed to the circuit 2.The transmit/receive means 3 are further arranged, by using the signalS, to generate a supply voltage V relative to a reference potential GNDfor parts of the circuit. The transmit/receive means 3 are furtherarranged to demodulate the received signal S, which is modulated in thiscase, and to emit enquiry data RD that is communicated by means of themodulated signal S received. The transmit/receive means 3 are furtherarranged to receive answer data AD and, for the purpose of transmittingthe answer data AD, to load modulate the received signal S, that isunmodulated in this case.

The circuit 2 also has data-processing means 4 that are implemented bymeans of a microprocessor, which microcomputer also has a memory. Thedata-processing means 4 are arranged to receive the enquiry data RD andto process the enquiry data RD and, as a function of the enquiry dataRD, to generate the answer data AD and to emit the answer data AD to thetransmit/receive means 3.

The circuit 2 further has storage means 5 that are arranged to storeinformation capacitively, the information being represented by a valueof an information voltage UI that arises at the storage means 5. Unlikethe information stored by the memory of the microprocessor, theinformation stored by the storage means 5 is intended to be availablemerely for a period of time and to temporarily indicate a communicationstatus occurring during a communication. The storage means 5 areimplemented in the form of a storage capacitor 5A shown in FIG. 2.

The circuit 2 further has information-voltage generating means 6 thatare arranged to receive a control signal CS, which control signal CS isof a voltage value UCS that is at most equal to the value of the supplyvoltage V. The information-voltage generating means 6 are furtherarranged to generate the information voltage UI by using the controlsignal CS. For this purpose, the information-voltage generating means 6have a charging-current generating stage 7 that is arranged to generateand emit a charging current for the storage means 5. As shown in FIG. 2,the charging-current generating stage 7 is implemented in the form of afirst n-channel field effect transistor 7A whose source terminal isconnected to the storage capacitor 5A. The charging-current generatingstage 7 further has a current source 7B that is arranged to generate thecharging current for the storage capacitor 5A and that is connected inseries with the first n-channel field effect transistor 7A between saidfirst n-channel field effect transistor 7A and the supply voltage V. Theinformation voltage UI can be picked off relative to the referencepotential GND at a point P in the circuit situated between theinformation-voltage generating means 6 and the storage means 5.

The information-voltage generating means 6 further have voltage-raisingmeans 8 that are arranged to receive the control signal CS and to raisethe value UCS of the voltage of the control signal CS. Thevoltage-raising means 8 are further arranged to emit a control signalCS′ of raised voltage. The information-voltage generating means 6further have voltage-limiting means 9 that are arranged between thevoltage-raising means 8 and the charging-current generating stage 7 andthat are arranged to receive the control signal CS′ of raised voltageand to emit a control signal CS2″ of limited voltage, which controlsignal CS2″ represents the control signal CS, to the charging-currentgenerating stage 7 or rather to the gate terminal of the first n-channelfield effect transistor 7A.

As shown in FIG. 2, the voltage-raising means 8 are implemented in theform of a charge pump 10, which charge pump 10 has a charge-pumpcapacitor 11, a first switch 12 and a second switch 13. The controlsignal CS can be fed to the two switches 12 and 13. The two switches 12and 13 are shown in a rest position in FIG. 2. The charge-pump capacitor11 is connected between the supply voltage V and the reference potentialGND, as a result of which the voltage applied to the charge-pumpcapacitor 11 assumes the value of the supply voltage V. If the controlsignal CS is received, the two switches 12 and 13 are arranged to switchover from their rest state to an active state, as is indicated in FIG. 2by broken lines. With the switches in this active state, the charge-pumpcapacitor 11 is connected between the voltage-limiting means 9 and thedata-processing means 4, which means that the voltage value UCS can beraised by the value of the supply voltage V at the input to thevoltage-limiting means 9. The two switches 12 and 13 are implemented inthe form of field effect transistors. The voltage-limiting means 9 areimplemented in the form of a diode configuration (not shown in FIG. 2),thus enabling the voltage value of the control signal CS′ of raisedvoltage to be limited to a value compatible with use in thecharging-current control stage 7.

This gives the advantage that the supply voltage V available can be usedin the optimum way to generate the information voltage U1.

The data carrier 1 shown in FIG. 1 further has evaluation means 14 towhich the information voltage UI arising at the point P in the circuitcan be fed and that, with the help of a comparison voltage UC, arearranged to evaluate the information voltage UI for the information thatis represented by said information voltage U1. The evaluation means 14are arranged to receive the comparison voltage UC. For the purpose ofgenerating the comparison voltage UC, the data carrier 1 hascomparison-voltage generating means 15 that are implemented separatelyfrom the evaluation means 14 and that are arranged to generate thecomparison voltage UC and emit it to the evaluation means 14.

The evaluation means 14 are implemented in the form of a differenceamplifier stage 16 as schematically indicated in FIG. 3. The differenceamplifier stage 16 has a first input 16A at which the informationvoltage UI can be fed to it. The difference amplifier stage 16 furtherhas a second input 16B at which the comparison voltage UC can be fed toit. The difference amplifier stage 16 further has a first output 16Cfrom which the difference amplifier stage 16 can emit the informationstored by means of storage means 5 in the form of information data ID.The information data ID represents a first logic state if the value ofthe information voltage UI is higher than the value of the comparisonvoltage UC and the information data ID represents a second logic stateif the value of the information voltage UI is lower than the value ofthe comparison voltage UC. The difference amplifier stage 16 further hasa third input 16D at which it is arranged to receive a controlling testsignal TS. The difference amplifier stage 16 further has a second output16E, at which second output 16E the difference amplifier stage 16 isarranged to emit a voltage representing the information voltage U1. Thecircuit 2 has a test terminal T connected to the second output 16E, fromwhich the voltage representing the information voltage UI can be pickedoff. Hence the evaluation means 14 are arranged to make the informationvoltage UI available at terminal T in a way that can be controlled bymeans of the test signal TS.

The difference amplifier stage 16 is shown in detail in FIG. 4. Thedifference amplifier stage 16 is implemented in the form of a firstp-channel field effect transistor 17 and a second p-channel field effecttransistor 18, with the control electrode of the first p-channel fieldeffect transistor 17 forming the first input 16A and the controlelectrode of the second p-channel field effect transistor 18 forming thesecond input 16B. The source terminals of the two p-channel field effecttransistors 17 and 18 are connected together and form the second output16E. Between the two p-channel field effect transistors 17 and 18 andthe supply voltage V is connected a current source 21. The drainterminals of the two p-channel field effect transistors 17 and 18 areconnected to a current mirror, which current mirror is implemented inthe form of a second n-channel field effect transistor 19 and a thirdn-channel field effect transistor 20. A third switch 22 is connectedbetween the reference potential GND and the drain terminal of the firstp-channel field effect transistor 17. A fourth switch 23 is connectedbetween the reference potential and the source terminal of the secondn-channel field effect transistor 19. A fifth switch 24 is connectedbetween the reference potential GND and the source terminal of the thirdn-channel field effect transistor 20. The three switches 22, 23 and 24are shown in their rest state. The three switches 22, 23 and 24 areimplemented in the form of further field effect transistors (not shownin FIG. 4) and, when the test signal TS is present, which test signal TSsets the three switches 22, 23 and 24 to their active state, thedifference amplifier stage 16 can be de-activated, by means of theswitches 22, 23 and 24, from evaluating the information voltage UI, as aresult of which a representation of the information voltage UI becomesavailable at the same time at the second output 16E. This gives theadvantage that the information voltage UI, or rather its waveform overtime, can be measured from outside the circuit 2 for test purposes. Inthe absence of the controlling test signal TS, the three switches 22 to24 are controlled to their rest state, and the voltage differencearising between the first input 16A and the second input 16B isavailable amplified, by so-called “open-loop amplification”, at thefirst output 16C in the form of the information data ID.

The comparison-voltage generating means 15 are arranged to take accountof a value of the supply voltage V by virtue of the fact that the valueof the comparison voltage UC that can be generated and emitted by thecomparison-voltage generating means 15 is proportional to the value ofthe supply voltage V. This gives the advantage that there is arelationship between the value of the information voltage UI and thevalue of the comparison voltage UC that does actually allow them to becompared with one another. The comparison-voltage generating means 15are further arranged to generate the comparison voltage UC in aprogrammable manner. For this purpose, the comparison-voltage [sic]generating means 15 are arranged to receive a programming signal PSthat can be generated and emitted by the data-processing means 4. Thisgives the advantage that the value of the comparison voltage UC can bevaried in a programmable manner, which enables the period of validity ofan item of information stored by means of the storage means 5 to beacted on because, if the value of the comparison voltage UC isrelatively high, any degradation of the information voltage UI caused byleakage currents will come into play at an earlier point in time thanwould be the case if the value of the comparison voltage were lower inrelative terms.

In what follows, the operation of the data carrier 1 will now beelucidated by reference to a first example of an application of the datacarrier 1 of FIG. 1.

In this example of an application it is assumed that thecommunication-related information that is to be stored for a period oftime by means of the storage means 5 is to represent a communicationstatus for a data carrier 1 that occurs in the event of ananti-collision communication, which status is used internally in thedata carrier 1 and serves to indicate that successful communication hasalready taken place between the data carrier 1 and the communicationdevice. An anti-collision communication of this kind is needed whenthere are a plurality of data carriers 1 present within a communicationarea of a communication device at the same time and the communicationdevice first has to determine the data carrier 1 with whichcommunication can be performed, with unique serial numbers stored in thedata carriers 1 being used to identify the data carriers 1.

Each of the data carriers 1, which is situated in a virtually staticposition in the communication area of the communication device, firstreceives the unmodulated signal S, as a result of which a supply voltageV for the circuit 2 is generated by means of the transmit/receive means3, thus enabling data to be processed in the data-processing means 4.The first thing this does is to cause the programming signal PS, whichsignal is intended for programming the comparison-voltage generatingmeans 15 to generate a comparison voltage UC, to be generated andemitted to the comparison-voltage generating means 15. The programmingsignal PS causes the comparison-voltage generating means 15 to generatea comparison voltage UIC whose value is equal to 0.25 times the value ofthe supply voltage V.

The communication device first puts out, by means of the signal S, aso-called GROUP SELECT command. This command is received by thetransmit/receive means 3 in each data carrier 1 and is emitted to thedata-processing means 4 in the form of enquiry data RD. Answer data ADis then emitted by the data-processing means 4 to the transmit/receivemeans 3, which answer data AD represents the serial number of the datacarrier 1.

The eventuality may occur in this case that a plurality of data carriers1 answer virtually simultaneously and in so doing produce loadmodulations of the signal S that correspond to their respective serialnumbers, in which case the communication device is then unable toreceive a valid serial number and emits a FAIL command. In the datacarriers 1, the enquiry data RD representing the FAIL command is thenprocessed by the data-processing means 4 and, on the basis of a randomnumber for example, then causes the data carriers 1 to emit their serialnumbers to the communication device in different time ranges, as aresult of which it is possible for the communication station torecognize each serial number unambiguously.

The serial number received by the communication device is used to readout the answer data AD from the data carrier 1, a READ WITH SERIALNUMBER command being sent to the data carrier 1 for this purpose, inwhich case only the data carrier 1 whose internally stored serial numbermatches the serial number received communicates answer data AD to thecommunication device.

It is precisely in this data carrier 1 that the control signal CS isgenerated by means of the data-processing means 4 and is emitted to theinformation-voltage generating means 6, the value of the voltage of thecontrol signal CS being equal to the value of the supply voltage V. Inthe information-voltage generating means 6, the value of the voltage ofthe control signal CS is raised by means of the voltage-raising means 8to twice the value of the supply voltage V. The control signal CS′ ofraised voltage that is obtained in this way is fed to thevoltage-limiting means 9, by means of which the value of the controlsignal CS′ of raised voltage is limited to a value which is equal to thevalue of the supply voltage V increased by 0.7 volts. Thevoltage-limited control signal CS″ obtained in this way is fed to thefirst n-channel field effect transistor 7A in the charging-currentgenerating stage 7 and drives it to the conducting state. The storagecapacitor 5A is then charged by means of the charging current fed fromthe current source 7B until such time as the value of the informationvoltage UI arising at point P in the circuit is virtually identical tothe value of the supply voltage V because the value of the voltage ofthe voltage-limited control signal CS″ is higher than the value of thesupply voltage V by 0.7 volts, or in other words by exactly thegate-source threshold voltage of the first n-channel field effecttransistor 7A. Hence, in the case of this data carrier 1, theinformation that successful communication has already taken place with acommunication station using the serial number of the data carrier 1 hasbeen stored by means of the storage means 5 using the full valueavailable of the supply voltage V.

However, because all the other data carriers 1 present are alsoendeavoring to achieve this status, the anti-collision communication iscarried out again until successful communication has taken place withall the data carriers 1 using their respective serial numbers. In theprocess, when the GROUP SELECT command is again received, theinformation data emitted by the evaluation means is first queried in thedata carrier 1 and there is no further participation in ananti-collision communication if the information data ID indicates thatthe value of the information voltage UI is higher than the value of thecomparison voltage UC.

The information represented by means of the information voltage UI isavailable temporarily after it has been generated, because it is subjectto degradation caused by the leakage currents in circuit 2. However,during this “life” of the information, the supply voltage can even dropbelow a critical value required for the supply of the data-processingmeans 4, which may happen in the course of the communication if forexample the data carrier 1 is briefly screened off from the signal S orif there is a frequency hopping process, without the information beinglost or becoming invalid during the life. Selecting a figure of 0.25times the value of the supply voltage V as a value for the comparisonvoltage UC ensures that even when there are a relatively large number ofdata carriers 1 within the communication area the life of the storedinformation will be long enough to outlast successful communication withall the data carriers 1.

It should be mentioned at this point that after successful communicationwith all the data carriers 1 the communication device puts out anINITIALIZE command that causes the information stored by means of thestorage means 5 to be deleted in all the data carriers 1 situated in thecommunication area of the communication device, which is done inconventional fashion by means of a deleting transistor (not shown inFIG. 1) by means of which the storage capacitor 5A is discharged.

In what follows, the operation of the data carrier 1 will now beelucidated by reference to a second example of an application of thedata carrier 1 of FIG. 1.

In this example of an application, it is assumed that a data carrier 1is in each case situated on a product and that a plurality of suchproducts are being moved on a conveyor belt at relatively high speedthrough two communication areas, belonging to two differentcommunication devices, which areas are arranged one behind the other inthe direction of movement and do not overlap one another.

In this case too an anti-collision communication has to be carried outif there are a plurality of data carriers 1 present in a communicationarea at the same time. However, to avoid the situation that, when thereis information stored in a data carrier 1 by means of the informationvoltage UI that successful communication has already taken place withthe first communication device, this information will still be validwhen the communication area of the second communication device is passedthrough, a comparison voltage UC whose value is equal to 0.75 times thevalue of the supply voltage V is generated by means of the programmingsignal on entry into the first communication area, i.e. that belongingto the first communication device.

This is a simple way of ensuring that the life of the information issufficiently short to ensure that, even if the INITIALIZE command is notreceived by the data carrier 1, the value of the information voltage UIwill be below the value of the comparison voltage UC on entry into thecommunication area of the second communication device. This ensures thatthe data carrier 1 cannot pass through the communication area of thesecond communication device without proper communication, i.e.anti-collision communication where required, taking place with it.

It should also be mentioned that the storage means may have a number ofstorage locations and that a number of information-voltage generatingmeans and evaluation means equal to the number of storage locations maybe provided.

It should further be mentioned that the signal may be phase-modulated orfrequency-modulated.

1. A data carrier that is arranged to receive a signal in anon-contacting manner and that has an electrical circuit, to whichcircuit the signal can be fed and which circuit is arranged, by usingthe signal, to generate a supply voltage for parts of the circuit, whichcircuit comprises storage means that are arranged to store informationcapacitively, the information being represented by a value of aninformation voltage arising at the storage means, and which circuitcomprises information-voltage generating means that are arranged toreceive a control signal, which control signal is of a voltage valuethat is at most equal to the value of the supply voltage, and that arearranged to generate the information voltage by using the controlsignal, characterized in that the information-voltage generating meanshave voltage-raising means that are arranged to raise the voltage valueof the control signal.
 2. A data carrier as claimed in claim 1,characterized in that the voltage-raising means are implemented in theform of a charge pump that is arranged to raise the voltage value of thecontrol signal by the value of the supply voltage.
 3. A data carrier 1as claimed in claim 1, characterized in that the information-voltagegenerating means have voltage-limiting means that are arranged to limitthe raising of the voltage value of the control signal.
 4. A circuit fora data carrier, which data carrier is arranged to receive a signal in anon-contacting manner, to which circuit the signal can be fed and whichcircuit is arranged, by using the signal, to generate a supply voltagefor parts of the circuit, which circuit comprises storage means that arearranged to store information capacitively, the information beingrepresented by a value of an information voltage UI arising at thestorage means, and which circuit comprises information-voltagegenerating means that are arranged to receive a control signal, whichcontrol signal is of a voltage value that is at most equal to the valueof the supply voltage, and that are arranged to generate the informationvoltage by using the control signal, characterized in that theinformation-voltage generating means have voltage-raising means that arearranged to raise the value of the voltage of the control signal.
 5. Acircuit as claimed in claim 4, characterized in that the voltage-raisingmeans are implemented in the form of a charge pump that is arranged toraise the voltage value of the control signal by the value of the supplyvoltage.
 6. A circuit as claimed in claim 4, characterized in that theinformation-voltage generating means have voltage-limiting means thatare arranged to limit the raising of the voltage value of the controlsignal.
 7. A circuit as claimed in claim 4, characterized in that thecircuit is implemented in the form of an integrated circuit.